Drop-in anchors for use in, for example, fastening items to masonry, typically include a sleeve, which is placed in a pre-drilled hole. A plug is driven into an expandable portion of the sleeve which, when expanded, secures the sleeve in the hole. Items may be secured to the masonry via a threaded end of the sleeve opposite the expandable portion of the sleeve.
In typical drop-in anchors, the plug is frustoconically shaped thereby providing an outer surface substantially matching an inwardly tapering inner wall of the sleeve. This has always been, understandably thought to be the most efficient configuration for a drop-in anchor as the angled surfaces have been understood to work with each other to garner the desired effect while using the angle to make insertion as easy as it can be. Nevertheless, drop-in anchors of the prior art require substantial setting force, normally obtained by the application of a relatively large number of blows with a sledge hammer. The art would well receive a drop-in anchor requiring a lower setting force to set the plug and expand the sleeve.